1. Field of the Invention
The present invention relates to a vehicular brake system. In particular, the present invention relates to a vehicular brake system for generating a wheel brake force greater than a brake force corresponding to depressing a brake pedal.
2. Description of Related Art
Load transfer in a vehicle chassis occurs during braking operations of a vehicle. Load transfer is influenced by the vehicle's deceleration which results in a gradual increase in the load on the front wheels of the vehicle. To deal with such problems, proportional control valves, for example, have been provided in the rear wheels to make pressure applied to the rear wheels lower than the pressure applied on the front wheels so that the brake forces generated on the rear wheels are lower than brake forces generated on the front wheels. These widely known proportional control valves reduce the amount of brake fluid in the direction of the brake fluid flow based on predetermined attenuation ratios.
When such a proportional control valve is provided, even if there is actually a high brake pressure in the master cylinder due to the demand for a high braking force, the brake pressure applied to the wheel cylinders is reduced by the proportional control valve which results in a smaller brake force. Thus, performance efficiency of the brake system declines because a significant amount of brake pressure is wasted when generating a large brake force.